Hammerhead sharks are some of the Ocean's most distinctive residents.‘Everyone wants to understand why they have this strangehead shape,’ says Michelle McComb from Florida AtlanticUniversity. One possible reason is the shark's vision. ‘Perhapstheir visual field has been enhanced by their weird head shape,’says McComb, giving the sharks excellent stereovision and depthperception. However, according to McComb, there were two schoolsof thought on this theory. In 1942, G. Walls speculated thatthe sharks couldn't possibly have binocular vision because theireyes were stuck out on the sides of their heads. However, in1984, Leonard Campagno suggested that the sharks would haveexcellent depth perception because their eyes are so widelyseparated. ‘In fact one of the things they say on TV showsis that hammerheads have better vision than other sharks,’says McComb, ‘but no one had ever tested this’.Teaming up with Stephen Kajiura and Timothy Tricas, the triodecided to find out how wide a hammerhead's field of view isand whether they could have binocular vision (p. 4010).

Hammerheads come in all shapes and sizes so McComb and Kajiura,opted to work with species with heads ranging from the narrowestto the widest. Fishing for juvenile scalloped hammerheads offHawaii and bonnethead sharks in the waters around Florida, theteam successfully landed the fish and quickly transported themback to local labs to test the fish's eyesight.

The team tested the field of view in individual shark's eyesby sweeping a weak light in horizontal and vertical arcs aroundeach eye and recorded the eye's electrical activity. Comparingthe hammerheads with pointy nosed species, the team found thatthe scalloped hammerheads had the largest monocular visual field,at an amazing 182 deg., and the bonnethead had a 176 deg. visualfield, which was bigger than that of the pointy nosed blacknoseand lemon sharks, at 172 deg. and 159 deg., respectively.

Having collected the animals’ monocular visual fields,the team plotted the visual fields of both eyes on a chart ofeach fish's head to see whether they overlapped. Amazingly,they did. The scalloped hammerhead had a massive binocular overlapof 32 deg. in front of their heads (three times the overlapin the pointy nosed species) while the bonnet head had a respectable13 deg. overlap. And when the team measured the binocular overlapof the shark with the widest hammerhead, the winghead shark,it was a colossal 48 deg. The hammerheads' wide heads certainlyimproved their binocular vision and depth perception.

Finally, the team factored in the sharks' eye and head movementsand found that the forward binocular overlaps rocketed to animpressive 69 deg. for the scalloped hammerheads and 52 deg.for the bonnetheads. Even more surprisingly, the team realisedthat the bonnethead and scalloped hammerheads have an excellentstereo rear-view: they have a full 360 deg. view of the world.

‘When we first started the project we didn't think thatthe hammerhead would have binocular vision at all. We thoughtno way; we were out there to dispel the myth,’ says McComb.But despite their preconceptions, the team have shown that thesharks not only have outstanding forward stereovision and depthperception, but a respectable stereo rear view too, which iseven better than the TV shows would have us believe.

ScienceDaily (Dec. 2, 2009) — Hit-and-run attacks by sharks can be solved with a new technique that identifies the culprits by the unique chomp they put on their victims, according to a University of Florida researcher and shark expert.

In a method analogous to analyzing human fingerprints, scientists can make identifications by precisely comparing shark bites to the jaws and teeth of the powerful predators, said George Burgess, director of the International Shark Attack File, which is housed at UF's Florida Museum of Natural History.

"Every time we investigate a shark attack one of the pieces of information that we want to have is what species was involved and what size it was," he said. "Because I've been looking at shark attack victims for 30 years I can estimate what did the damage, but I have never been able to actually prove it."

Now scientists can say with a degree of certainty whether the beast was a 14-foot tiger shark or a 9-foot bull shark, a distinction that has unforeseen emotional, ecological and even monetary benefits, said Burgess, who collaborated with researchers from the University of South Florida. Their findings are published in the November issue of Marine Biology.

"There's a psychological need for many shark attack victims to know what bit them," Burgess said. "One of the few things shark attack victims have going for them after a bite is bragging rights and the bragging rights include knowing what did the damage."

Because of the hype surrounding shark attacks, off-the-cuff estimates of shark size are often exaggerated, he said. "This will give an actual basis for determining what species was involved and the size, not that that's going to affect the size claimed by the victim in a bar," he said.

Using dried shark jaws from museums and private collections, the researchers were able to identify bite patterns of particular sizes and species of sharks by measuring jaw circumference and the distance between the six frontal teeth on the top and lower jaws, Burgess said. They experimented on 10 to 24 sets of shark jaws for each of the 14 species they analyzed. The technique works not only on human and animal tissue, but also on inanimate objects like surfboards and underground cable lines, he said.

The ability to make predictions from bite patterns is important to understanding the behavioral underpinnings of shark attacks and their prey habits, said lead researcher Dayv Lowry, a biologist with the Washington Department of Fish and Wildlife, who did the work as a graduate student at the University of South Florida.

"Often someone will send us a picture of a dolphin carcass or a sea turtle and want to know what kind of shark bit it," Lowry said. "Knowing that it's a large tiger shark, for example, would help us figure out what large tiger sharks like to eat and how they attack their prey. If an animal or person has been bitten on the rear end, then we know these sharks are likely to sneak up to get their prey instead of facing the victims."

Being able to determine what size shark attacked people in certain geographic areas such as South Africa where offshore nets are used to protect swimmers is valuable because it may influence the size mesh that is used, Lowry said. With larger sharks, beaches can get by with bigger mesh sizes, which are cheaper and less environmentally intrusive, he said.

The technique also has the potential to save thousands of dollars in damages caused by the sharks' penchant for attacking underwater electronic equipment, which includes intercontinental telephone wires, top-secret communication lines between government officials and sensors companies use to uncover oil fields, Burgess said.

Sharks are equipped with organs on the underside of their snouts -- gel filled pits called ampullae of Lorenzini -- that allow them to detect electromagnetic fields from their intended food, Burgess said. Unfortunately, sharks often do not distinguish between the signals sent by prey and equipment, which can be ruined by water seeping in through the bite marks, he said.

"That's one thing that makes them special -- they can sense electro-magnetic fields around their prey items," he said.

Laying cable lines at the bottom of the ocean is extremely expensive, and having to remove a piece, fix it and install it again adds to the cost, Burgess said. "Knowing that a certain species of shark did the damage is useful because in the future cable lines can be placed in a different location, outside the path of that particular shark's area of distribution," he said.

And the ability to determine what size shark was involved in an attack by the size and configuration of its bite marks could result in the installation of a heavier seal designed to withstand damage from that kind of shark, he said.

Shark Fins Traced to Their Geographic Origin for First Time Using DNA Tools

ScienceDaily (Dec. 2, 2009) — Millions of shark fins are sold at market each year to satisfy the demand for shark fin soup, a Chinese delicacy, but it has been impossible to pinpoint which sharks from which regions are most threatened by this trade. Now, groundbreaking new DNA research has, for the first time, traced scalloped hammerhead shark fins from the burgeoning Hong Kong market all the way back to the sharks' geographic origin. In some cases the fins were found to come from endangered populations thousands of miles away.

Published online December 1 in the journal Endangered Species Research, the findings highlight the need to better protect these sharks from international trade, a move which will be considered by the Convention on International Trade in Endangered Species (CITES) at its March 2010 meeting in Qatar. The work was led by the Guy Harvey Research Institute and the Save Our Seas Shark Center at Nova Southeastern University and the Institute for Ocean Conservation Science at Stony Brook University.

The U.S. has proposed that CITES list the scalloped hammerhead and five other shark species under the organization's Appendix II, which would require permits for, and monitoring of, all trade in these species across international boundaries. Knowing the species and geographic origin of fins being traded would allow management and enforcement efforts to be allocated more effectively.

"Although we've known that a few million hammerhead shark fins are sold in global markets, we now have the DNA forensic tools to identify which specific hammerhead species the fins originate from, and in the case of scalloped hammerheads, also what parts of the world these fins are coming from," said Dr. Mahmood Shivji, senior author on the paper and Director of the Guy Harvey Research Institute (GHRI) and Save Our Seas Shark Center, both at Nova Southeastern University (NSU) in Florida. "This trade has operated for years and years under the cover of darkness," added lead author, Dr. Demian Chapman, now with the Institute for Ocean Conservation Science at Stony Brook University (SBU) in New York. "Our work shows that the scalloped hammerhead fin trade is sourced from all over the globe and so must be globally tracked and managed."

The new research paper is published in a special theme issue of Endangered Species Research entitled, "Forensic Methods in Conservation Research." Using CSI-like methods known as "genetic stock identification" or GSI, Drs. Chapman and Shivji along with Danillo Pinhal of the GHRI and Universidade Estadual Paulista, Brazil, analyzed fingernail-sized DNA samples from 62 scalloped hammerhead shark fins that had been obtained in the Hong Kong fin market. By examining each fin's mitochondrial DNA sequence -- a section of the genetic code passed down by the mother and traceable to a sharks' regional birthplace -- the researchers were able to exactly match 57 of the 62 fins to an Atlantic or Indo-Pacific ocean origin.

The team also analyzed mitochondrial sequences taken from 177 live scalloped hammerheads in the Western Atlantic and determined that the species is further divided into three distinct stocks in this region: northern (U.S. Atlantic and Gulf of Mexico), central (Belize and Panama), and southern (Brazil). The scientists traced 21 percent of the Hong Kong fins back to these Western Atlantic stocks. Scalloped hammerheads in the region have been categorized as endangered by the IUCN (International Union for the Conservation of Nature) since 2006. This coastal species appears to have collapsed in the western North Atlantic and Gulf of Mexico.

"The premium prices commanded by fins have fueled a global shark hunt of epic proportion," said Dr. Ellen Pikitch, Executive Director of the Institute for Ocean Conservation Science at SBU, which funded a portion of the research. "Earlier work found that up to 73 million sharks are killed annually to supply the fin markets, and approximately 1-3 million are hammerheads," said Dr. Pikitch, who is also a Professor of Marine Science at Stony Brook University. "Inadequate protection, combined with inexorable pursuit, has placed many shark species at grave risk." Just 1 kg (2.2 lbs) of scalloped hammerhead fin can sell for about $US120 at Hong Kong markets due to the large size and high "fin needle" content of this species' fins. Needles are the sought-after portion of the fins, used as thickener in the soup.

"The fact that scalloped hammerhead shark DNA shows strong population DNA signatures means that we can trace the geographic origin of most of their fins sold at markets," Dr. Shivji said. "From a broader perspective, this type of DNA forensic testing of fins will be an incredibly useful tool to prioritize areas for conservation and ensure sharks aren't wiped out in particular regions by excessive fishing."

This study builds upon a DNA test developed in 2005 at the Guy Harvey Research Institute by Dr. Shivji and Debra Abercrombie, a research scientist now with the Institute for Ocean Conservation Science at SBU. The test enabled scientists to rapidly and definitively distinguish between three similar hammerhead species: great, scalloped, and smooth, from fin or meat tissues alone. The new GSI technique takes that DNA test to the next level. GSI has been used to trace some fish, sea turtle and marine mammal catches back to their geographic origin. This study marks its first use with sharks. Dr. Chapman is now working on DNA tools to identify a shark's geographic origins even more precisely, while both he and Dr. Shivji are working on developing GSI for more shark species, including other large hammerheads.

"The international shark fin trade must not continue to operate in secrecy," Dr. Chapman said. "We must use all tools available -- from CITES permitting to DNA tests -- to shed light on this trade and make sure that it does not drive these sharks to extinction." Drs. Pikitch and Chapman plan to attend the CITES meeting in Qatar in March to urge that these sharks be listed under Appendix II to receive better protection from trade.

This research was funded by the Institute for Ocean Conservation Science at SBU, the Guy Harvey Research Institute at NSU and the Save Our Seas Foundation.